In-plane switching mode liquid crystal display device and method for manufacturing the same

ABSTRACT

An in-plane switching mode LCD device and a method for manufacturing the same are disclosed, which are applicable to LCD device having a wide viewing angle, fineness and a wide size by using low resistance materials as source and drain electrode. A buffer layer is formed on an ohmic contact layer in the in-plane switching mode LCD.

This application claims the benefit of Korean Patent Application No.2000-81949, filed on Dec. 26, 2000, the entirety of which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device, and moreparticularly, to an in-plane switching mode liquid crystal display (LCD)device and a method for manufacturing the same.

2. Background of the Related Art

An in-plane switching mode LCD device is an LCD device having a wideviewing angle, which has been developed for solving a problem of havinga narrow viewing angle in a Twisted Nematic LCD device. In the in-planeswitching mode LCD device, common and pixel electrodes are formed on onesubstrate, and liquid crystals are driven by a horizontal electric fieldgenerated between the common and pixel electrodes, so that a viewingangle in the in-plane switching mode LCD device is wider than a viewingangle in the Twisted Nematic LCD device.

A related art LCD device structure and a method for manufacturing thesame will be described with reference to the accompanying drawings.

FIG. 1A is a structural plan view illustrating a structure of therelated art in-plane switching mode LCD device. FIG. 1B is a plan viewtaken along line I–I′ of FIG. 1A.

As shown in FIG. 1A, the related art in-plane switching mode LCD deviceincludes gate line 211 and data line 212 arranged on an insulatingsubstrate (not shown) to define a pixel region, a common line 213arranged within the pixel region in parallel with the gate line 211, athin film transistor formed at a crossing point between the gate line211 and the data line 212, a pixel electrode 208 arranged within thepixel region in parallel with the data line 212 and connected with adrain electrode of the thin film transistor, and a common electrode 210arranged within the pixel region in parallel with the data line 212 andextending from the common line 213.

The thin film transistor will be described in detail with reference toFIG. 1B. A gate electrode 202 is formed on an insulating substrate 201,and a gate insulating film 203 is formed on the surface of theinsulating substrate 201 including the gate electrode 202. Then, asemiconductor layer 204 is formed like an island on the gate insulatingfilm 203 above the gate electrode 202, and an ohmic contact layer 205 isformed on both sides of the gate electrode 202 on the semiconductorlayer 204. Source electrode 206 and drain electrode 207 are formed atboth sides of the gate electrode 202 above the semiconductor layer 204.An ohmic contact layer 205 is formed between the source and drainelectrodes 206 and 207 and the semiconductor layer 204. A pixelelectrode 208 is formed on the drain electrode 207 and the gateinsulating film 203. A passivation film 209 is deposited on the gateinsulating film on which the pixel electrode 208 is formed, and a commonelectrode 210 is formed on the passivation film 209.

Generally, in the related art LCD device shown in FIG. 1B, the gateinsulating film 203 and the passivation film 209 may consist of asilicon nitride film (SiN_(x)). The gate electrode 202 may consist ofconductive materials such as copper (Cu), titanium (Ti), and chromium(Cr). The source electrode 206 and the drain electrode 207 may consistof chromium (Cr) in taking into consideration of the etching selectivitywith a transparent electrode.

A method for manufacturing the related art in-plane switching mode LCDdevice will now be described with reference to FIG. 2A to FIG. 2E.

FIG. 2A to FIG. 2E are plan views illustrating process steps formanufacturing the related art in-plane switching mode LCD device.

As shown in FIG. 2A, gate line materials and conductive metal materials,are deposited on the insulating substrate 201 by a process such assputtering. Then, the gate electrode 202 is formed by a patterningprocess such as photolithography. The gate insulating film 203consisting of a silicon oxide film or a silicon nitride film, thesemiconductor layer 204 of amorphous silicon, and the ohmic contactlayer 205 of amorphous silicon containing n-type dopant, are depositedby a process such as plasma enhanced chemical vapor deposition (PECVD).

As shown in FIG. 2B, the semiconductor layer 204 and the ohmic contactlayer 205 formed on the gate insulating film 203, are selectivelypatterned.

As shown in FIG. 2C, a data line material, a conductive metal materialsuch as chromium (Cr), is deposited on the ohmic contact layer 205 by asputtering process, and the source electrode 206 and the drain electrode207 are formed by a patterning process such as photolithography, so thatthe thin film transistor is formed.

As shown in FIG. 2D, the pixel electrode 208 is formed on the drainelectrode 207.

As shown in FIG. 2E, the passivation film 209 is deposited on thesubstrate, on which the above layers are deposited, by a plasma enhancedchemical vapor deposition (PECVD) process. The transparent commonelectrode 210 is formed on the passivation layer 209 using a conductivematerial such as indium tin oxide (ITO). Therefore, the manufacturingprocess steps of the related art LCD device are completed.

However, there are following problems in the related art in-planeswitching mode LCD device.

First, the pixel electrode occupies space within the pixel region andso, an aperture ratio is reduced by an area occupied by the pixelelectrode.

The pixel electrode connected with the drain electrode can be formed asthe transparent electrode for solving the problem of a decrease in theaperture ratio. However, if etching selectivity between the transparentelectrode and the drain electrode is not considered, the drain electrodemay be etched during patterning of the transparent electrode. Therefore,reliability of the device may be degraded.

Furthermore, if the drain electrode material is selected taking intoconsideration the etching selectivity ratio between the transparentelectrode and the drain electrode, chromium is the most appropriatematerial for the drain electrode.

But, since chromium has low electricity conductivity, and especiallyaffects resolution, there are limitations in implementing the in-planeswitching mode LCD device having high resolution and a large size.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an in-plane switchingmode LCD device and a method for manufacturing the same whichsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An advantage of the present invention is to provide an in-planeswitching mode LCD device and a method for manufacturing the same thatare applicable to an LCD device having high resolution and a large sizeby improving brightness and aperture ratio without an additional mask.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, the in-planeswitching mode liquid crystal display device comprises a thin filmtransistor within a pixel region defined by a plurality of gate linesand data lines; and buffer layer is interposed between a gate electrodeand source and drain electrodes of the thin film transistor. The activeregion includes a gate electrode on an insulating substrate; a gateinsulating film on an entire surface of the insulating substrateincluding the gate electrode; a semiconductor layer and an ohmic contactlayer on the gate insulating film; a buffer layer on the ohmic contactlayer to cover the semiconductor layer and the ohmic contact layer;source and drain electrodes on the buffer layer; a transparentconductive film for a pixel electrode connected with the drainelectrode; a passivation film on the pixel electrode; and a commonelectrode on the passivation film.

In another aspect of the present invention, a method for manufacturingthe in-plane switching mode LCD device includes selectively depositing abuffer layer on the insulating substrate deposited on the gateelectrode, the gate insulating film, the semiconductor layer, and theohmic contact layer; patterning the buffer layer; forming thetransparent conductive film for the pixel electrode through the gateinsulating film and the buffer layer; and forming the source and drainelectrodes to connect with the transparent conductive film for the pixelelectrode.

In the in-plane switching mode LCD device according to the presentinvention, the buffer layer is formed on the ohmic contact layer, sothat the etching selectivity between the drain electrode and thetransparent conductive film is improved and it is possible to preventthe drain electrode from chemically reacting with the ohmic contactlayer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1A is a plan view illustrating a structure of a related artin-plane switching mode LCD device;

FIG. 1B is a plan view taken along line I–I′ of FIG. 1A;

FIG. 2A to FIG. 2E are sectional views illustrating manufacturingprocess steps in accordance with the related art in-plane switching modeLCD device;

FIG. 3 is a sectional view illustrating a structure of an in-planeswitching mode LCD device in accordance with the present invention; and

FIG. 4A to FIG. 4E are sectional views illustrating manufacturingprocess steps of the in-plane switching mode LCD device in accordancewith the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to an embodiment of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

Since a plan structure of an LCD device according to the presentinvention is the same as a structure of a related art LCD device, theplan structure of the LCD device according to the present invention willbe described with reference to the related art plan view.

FIG. 3 is a sectional view illustrating a structure of an in-planeswitching mode LCD device in accordance with the present invention,taken along line I–I′ of FIG. 1A. As shown in FIG. 3, the in-planeswitching mode LCD device according to the present invention includes aninsulating substrate 401; a gate electrode 402 formed on the insulatingsubstrate 401; a gate insulating film 403 formed on the insulatingsubstrate 401 including the gate electrode 402; a semiconductor layer404, an ohmic contact layer 405 and a buffer layer 406 deposited on thegate insulating film 403 at an upper portion of the gate electrode 402;a transparent pixel electrode 407 connected with the buffer layer 406;source electrode 408 and drain electrode 409 formed on the buffer layer406; a passivation layer 410 formed on an entire surface of theinsulating substrate 401 including the source electrode 408 and drainelectrode 409; and a common electrode 411 formed on the passivationlayer 410.

The gate electrode 402 is formed of a low resistance metal such asaluminum (Al), copper (Cu), and silver (Ag).

The gate insulating film 403 is formed of a silicon nitride film(SiN_(x)), or a silicon oxide film (SiO_(x)) and the buffer layer 406 isgenerally formed of metal such as titanium (Ti).

As the buffer layer is formed, it is possible to prevent low resistancemetals used as the source and drain electrodes from chemically reactingwith the ohmic contact layer, and an etching selectivity between thesource and drain electrodes and the transparent pixel electrode isimproved.

The manufacturing process steps of the in-plane switching mode LCDdevice will be described in more detail with reference to FIG. 4A toFIG. 4E.

As shown in FIG. 4A, one of the low resistance metals such as aluminum(Al), copper (Cu), and silver (Ag) is deposited on the insulatingsubstrate 401 by a sputtering process, and then the gate electrode 402is formed by a patterning process using photolithography. The gateinsulating film 403 comprising a silicon nitride film or a silicon oxidefilm is formed on the insulating substrate 401 including the gateelectrode 402. The semiconductor layer 404, the ohmic contact layer 405,and the buffer layer 406 of titanium are formed on the gate insulatingfilm 403 by a PECVD process. At this time, the presence of the bufferlayer 406 makes it possible to prevent the ohmic contact layer fromchemically reacting with a drain electrode, which will be formed.

As shown in FIG. 4B, the semiconductor layer 404, the ohmic contactlayer 405 and the buffer layer 406 of titanium, which are formed on thegate insulating film 403, are patterned. Then, as shown in FIG. 4C, thetransparent conductive film for the pixel electrode, such as ITO, isformed on the buffer layer 406 by a sputtering process, and is patternedso that a transparent electrode 407 is formed.

As shown in FIG. 4D, the source and drain electrodes 408 and 409 areformed of one of aforementioned low resistance metals to connect withthe transparent electrode 407 for the pixel electrode on the bufferlayer 406.

As shown in FIG. 4E, the passivation layer 410 is deposited on theentire surface of the insulating substrate 401 including the source anddrain electrodes 408 and 409, and then the common electrode 411 isformed on the passivation layer 410.

Afterwards, a liquid crystal layer is formed between the insulatingsubstrate 401 and an opposing substrate provided with a color-filter anda black matrix (not shown), so that the manufacturing process steps ofthe in-plane switching mode LCD device according to the presentinvention are completed.

As has been explained, the in-plane switching mode LCD device and themethod for manufacturing the same according to the present inventionhave the following advantages.

In the in-plane switching mode LCD device according to the presentinvention, brightness and aperture ratio can be improved without anadditional mask. Also, the buffer layer comprising titanium (Ti) isdeposited on the ohmic contact layer, so that the etching selectivitybetween the source and drain electrodes and the transparent conductivefilm is improved, and the buffer layer makes it possible to prevent achemical reaction between the source and drain electrodes and the ohmiccontact layer. Accordingly, the low resistance materials such asaluminum (Al), copper (Cu) and silver (Ag), can be used as the sourceand drain electrodes, so that the in-plane switching mode LCD device isapplicable to the LCD device having fineness and a large size.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An in-plane switching mode liquid crystal display (LCD) device comprising: a gate electrode on a substrate; a gate insulating film on an entire surface of the substrate; a semiconductor layer and an ohmic contact layer on the gate insulating film; a buffer layer on the ohmic contact layer; a pixel electrode on the buffer layer; source or drain electrodes on the pixel electrode, the source or drain electrodes being connected with a portion of the pixel electrode on the buffer layer, wherein the connection is at an overlap of the source or drain electrodes and an end portion of the buffer layer; a passivation layer on the entire surface of the substrate including the pixel electrode; and a common electrode on the passivation layer substantially parallel to the pixel electrode.
 2. The in-plane switching mode LCD device as claimed in claim 1, wherein the gate electrode includes a low resistance material.
 3. The in-plane switching mode LCD device as claimed in claim 2, wherein the low resistance material includes one of aluminum (Al), copper (Cu), and silver (Ag).
 4. The in-plane switching mode LCD device as claimed in claim 1, wherein the buffer layer includes a metal.
 5. The in-plane switching mode LCD device as claimed in claim 4, wherein the buffer layer includes titanium (Ti).
 6. The in-plane switching mode LCD device as claimed in claim 1, wherein the source and drain electrodes include a low resistance material.
 7. The in-plane switching mode LCD device as claimed in claim 6, wherein the low resistance material includes one of aluminum (Al), copper (Cu), and silver (Ag).
 8. The in-plane switching mode LCD device as claimed in claim 1, wherein the pixel electrode includes transparent conductive material.
 9. The in-plane switching mode LCD device as claimed in claim 8, wherein the pixel electrode includes indium tin oxide.
 10. The in-plane switching mode LCD device as claimed in claim 1, wherein the common electrode includes indium tin oxide.
 11. A method for manufacturing an in-plane switching mode liquid crystal display (LCD) device comprising: forming a gate electrode on a substrate; forming a gate insulating film, a semiconductor layer, an ohmic contact layer, and a buffer layer on the gate electrode; forming a pixel electrode on the buffer layer; forming a source electrode or a drain electrode on a portion of the pixel electrode on the buffer layer, the source or drain electrodes being connected with the pixel electrode at an overlap of the source or drain electrodes and an end portion of the buffer layer; forming a passivation layer on the entire surface of the substrate including the pixel electrode; and forming a common electrode on the passivation layer substantially parallel to the pixel electrode.
 12. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the gate electrode includes one of aluminum (Al), copper (Cu), and silver (Ag).
 13. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the buffer layer includes titanium (Ti).
 14. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the source and drain electrodes include one of aluminum (Al), copper (Cu), and silver (Ag).
 15. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the pixel electrode includes indium tin oxide.
 16. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the drain electrode is electrically connected with the pixel electrode.
 17. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the common electrode includes indium tin oxide.
 18. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the gate electrode is deposited by a sputtering process.
 19. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 18, wherein the gate electrode is patterned using photolithography.
 20. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 11, wherein the semiconductor layer, the ohmic contact layer, and the buffer layer are formed on the gate insulating film by a plasma enhanced chemical vapor deposition (PECVD) process.
 21. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 20, wherein the semiconductor layer, the ohmic contact layer, and the buffer layer are patterned.
 22. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 9, wherein the pixel electrode is formed by a sputtering process.
 23. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 22, wherein the pixel electrode is patterned.
 24. The method for manufacturing an in-plane switching mode LCD device as claimed in claim 9, wherein the passivation layer is formed by a deposition process. 